Imaging skyrmions in synthetic antiferromagnetic multilayers

Skyrmions are circular magnetic domains/domain walls in magnetic materials and have attracted great interest recently for spintronic applications. By the nature of the materials the skymrions possess a property known as topological protection, which means that they are hard to annihilate when they interact. Additionally when they are formed in multilayer films with antiferromagnetic coupling between the magnetic layers they have no skyrmion Hall angle, so when a spin polarised current is used to move them they move with the direction of charge flow without deviation. The size of the skymrions depend crucially on the multilayer composition in terms of layer composition and thickness etc. In this project skyrmions in different materials systems will be studied. The materials will be characterised by the methods of transmission electron microscopy (TEM) with the magnetic structure imaged by Lorentz imaging modes. Deposition of films will be carried out at the University of Leeds and the characterisation will be performed at the University of Glasgow. Skymrions with sizes less than 100 nm are to be studied.

In a continuous thin film system skyrmions tend to form at random positions at a certain nucleation field. Using various approaches we aim to nucleate site specific single isolated skyrmions. This is proposed via localised nanostructured defects and manipulation of the magnetic anisotropy at surface sites. In situ imaging will reveal that site specific nucleation of skyrmions is possible. We will also explore then moving the skyrmions with spin polarised currents to demonstrate possibilities for device application. In addition to TEM work beamline experiments will also be carried out to complement the TEM imaging. The project also involves working with colleagues at the National Physical Laboratory who are also interested in imaging via scanning probe microscopy.

This project aligns with EPSRC priorities in investigating new and advanced materials systems for spintronics applications. For example this materials system is a complex multilayer with magnetic and non magnetic layers possessing 3 different magnetic exchange interactions to provide the right environment for skyrmion stabilisation. In principle skyrmions down to a few 10s of nanometres can provide dynamic devices with controllable moving magnetic "bits", but without mechanical moving parts. This could be implemented logic devices or memory storage.